Some occupant leg restraining devices for preventing the lower legs of occupants from striking against interior panels in front of seats in the event of frontal collisions of fast moving bodies such as automobiles include an airbag disposed inside an interior panel (in a space behind the interior panel), a gas generator for inflating the airbag, a retainer that accommodates and holds the airbag and the gas generator at normal times (while a fast moving body such as an automobile is not involved in a collision), and a lid that is disposed over a rear opening of the retainer so as to cover the airbag.
In such an occupant leg restraining device, the airbag is usually folded and accommodated in the retainer inside the interior panel, and the lid is disposed over the rear opening of the retainer so as to cover the folded airbag during normal times. When an automobile or the like is involved in a frontal collision, the gas generator ejects gas. The gas is supplied to the airbag, and the lid is opened in response to the expansion of the airbag. With this, the airbag can expand toward the exterior of the interior panel, and can be deployed between the interior panel and the lower legs of an occupant, thereby preventing the lower legs of the occupant from striking against the interior panel (hereinafter, an airbag of this type expanding in front of the occupant legs is referred to as a knee airbag).
In a known occupant leg restraining device for a driver, a case (retainer) for a knee airbag is composed of sheet metal, and is disposed below a steering column. The case includes a peripheral wall having a substantially rectangular tube shape, a bottom wall (bottom plate) that closes an opening of the peripheral wall that faces the front side of a vehicle, and a substantially rectangular opening that faces the rear side of the vehicle. In addition, a right wall portion (side wall portion) of the peripheral wall has a through-hole through which an inflator (gas generator) can pass, whereas a left wall portion (side wall portion) of the peripheral wall is closed (see Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-206068 (Page 4, FIG. 3)